1. Field of the Invention
The present invention relates to an image processing device, an endoscope system and a method for operating an image processing device, that generate an image obtained by imaging an object in a subject body.
2. Description Related to the Prior Art
In medical fields, diagnoses utilizing endoscope systems have been widely performed. The endoscope system comprises a light source device, an endoscope, and a processor device. In the endoscope system, illumination light is applied from an endoscope to a region of interest (object), and an image of the object is displayed on a monitor based on an image signal obtained by imaging the object illuminated with the illumination light. A doctor detects the presence or absence of a lesion while observing the image displayed on the monitor.
It is known that gastric (stomach) cancer causes atrophy of gastric mucosa, which makes the color of the gastric mucosa to fade. For this reason, there is a difference in color between the atrophic mucosa and the normal mucosa. The stomach cancer is diagnosed by observing the difference in color between the suspected lesion and the normal portion with an endoscope. “ABC method (ABC screening)” is recommended by the authorized nonprofit organization “Japan Research Foundation of Prediction, Diagnosis and Therapy for Gastric Cancer”.
In advanced stages of atrophy (for example, groups C or D in the ABC screening), the difference in color between the normal portion and the atrophic portion is clear, so that it is easy to detect the atrophic portion. However, in intermediate stages (for example, groups B and C in the ABC screening), there is little difference in color between the atrophic portion and the normal portion. Therefore it is difficult to detect the atrophic portion based only on the difference in color.
In consideration of the above problem, United States Patent Application Publication No. 2016/0007829 (corresponding to Japanese Patent Publication No. 5647752) performs a color difference enhancing process which increases a difference between first and second signal ratios in a first color range and first and second signal ratios in a second color range to enhance a color difference between an atrophic portion and a normal portion, in a space formed by the first signal ratio between image signals of two colors out of three color image signals and a second signal ratio between image signals of two colors different from the first signal ratio.
However, the diagnosis of the lesion should be made in consideration of vascular states such as vascular patterns, in addition to the color difference between the normal portion and the lesion. Accordingly, in addition to enhance the color difference between the normal portion and the lesion as in United States Patent Application Publication No. 2016/0007829, it is required to emphasize blood vessels in an object and improve vascular visibility.